In a conventional optical disc system, to sense the position of the laser beam in relation to the track on the disc, the main laser beam creates a reflection from the disc. The reflection is typically picked up by 4 photo-diode sensors. FIG. 1 is a conceptual diagram illustrating how such a photo-diode configuration is laid out in relation to the track direction. The outputs of the 4 photo-diodes (when the laser beam is focused on the disc) are shown as signals A, B, C and D, respectively.
To control the position of a main laser beam 22 on the optical disc 23, the position of the objective lens 24 of the Optical Pickup Unit (OPU) 25 related to the tracks 26a-26n on the optical disc 23 is controlled by a tracking actuator. The OPU 25 is a device configured to emit a laser beam 22 and pick up the optical reflection of the beam 22. The OPU 25 converts such reflections to electrical signals. The position of the lens 24 and a housing 28 of the, OPU 25 are controlled by a stepper motor (not shown). The stepper motor moves the whole OPU 25. FIG. 2 illustrates the motion of the OPU 25 and the lens 24.
To direct the laser beam 22 to a particular one of the tracks 26a-26n of the optical disc 23, or to cross the tracks 26a-26n of the optical disc 23, the tracking actuator and the stepper motor are controlled at the same time. The tracking actuator controls the position of the lens 24 in relation to the optical disc 23. The stepper motor controls the position of the lens 24 in relation to the lens housing 28.
Control of the stepper motor is based on the same method used in controlling a DC motor. A conventional approach to control the stepper motor uses the bias force of the tracking actuator to sense the position of the lens 24 in the housing 28. Such a conventional approach will direct the motion of the stepper motor appropriately when the tracking actuator controls the laser beam 22. The tracking actuator will direct the motion of the laser beam 22 when the laser beam 22 stays on a particular one of the tracks 26a-26n, or when the laser beam 22 moves across the tracks 26a-26n. 
When the laser beam 22 stays on a particular one of the tracks 26a-26n, the laser beam 22 should be balanced. The balancing is accomplished by positioning the center of the laser beam 22 on the center of a particular one of the tracks 26a-26n. Positioning the center of the laser beam 22 on the center of the particular one of the tracks 26a-26n improves the quality of the signal picked up from the optical disc 23 to perform either reading or recording on the optical disc 23. With conventional approaches, the bias force of the tracking actuator cannot handle the balance of the laser beam 22 when the laser beam 20 is positioned on the particular one of the tracks 26a-26n. 
It would be desirable to provide a method and/or apparatus to improve the balance of a laser beam when the laser beam is positioned on the particular track through control of the stepper motor.